The present invention relates to a system for prioritizing fluid flow or pressure directed to a plurality of implements in a flow-share arrangement.
Hydraulic systems which receive an input flow and correspondingly provide multiple output flows, albeit in a controlled, predetermined priority are well known. Such hydraulic circuits are desirable and commonly employed in association with machines which are capable of performing multiple simultaneous or contiguous functions. For instance, a priority circuit may be employed in a hydraulic system of an earthmoving machine to orchestrate pressure and/or flow control between a steering system and an implement system as the two systems are simultaneously commanded. Without this priority scheme provided by the hydraulic system, steering control may be rendered ergonomically unmanageable as the operator positions, activates or otherwise animates the implement.
A typical hydraulic circuit, having flow prioritizing capabilities, generally includes a pump in fluid communication with priority and non-priority implements through a priority valve. The priority valve is in fluid communication with a signal line which urges the valve to modulate pump flow between priority and non-priority implements. The signal line is attached to a priority supply port of the priority valve and is diverted into a dynamic load signal line and a load signal line. The load signal line and a priority implement signal line is attached to the dynamic load signal. A bleed valve is installed in the load signal line to accordingly stabilize signal pressure. A shuttle valve is typically positioned upstream of the bleed valve to prevent the load signal from disrupting the dynamic load signal.
The shuttle valve is typically configured to provide signal flow to the pump from either the dynamic load signal or the load signal. However, during high load use of the priority valve a non-priority signal margin becomes unstable since fluctuations in load of the priority supply, are not communicated to the non-priority implements. Consequently, the non-priority implements are rendered inoperable or difficult to operate when a high demand is in effect on the priority implement.
Alternatively, a second type of priority valve, similar to the previously described priority valve, has previously been used. However rather than employing the shuttle valve in the load signal line, a check valve is provided upstream of the bleed valve. Consequently, the dynamic load signal is prone to significant parasitic loss which may be at least partially attributable to a fluctuating load signal. As a result, when the priority implement is under command and the dynamic load signal is substantially below a suitable value, the operation of the priority implement is adversely affected. For instance, if the priority implement is a hand metering unit (HMU), such as a steering valve, and the dynamic load signal has suffered a significant loss, an operator would likely experience difficulty (i.e., xe2x80x9chard spotsxe2x80x9d) as he or she attempted to turn the steering wheel.
Therefore, a priority valve system which includes a dynamic load signal not significantly influenced by the load signal, or any other influence, is desirable. Furthermore, a priority valve system which is configured to provide a controllable non-priority signal margin during high load priority function operation is desirable. Moreover, a priority valve arrangement capable of prioritizing flow, pressure or a combination thereof in a multiple implement system arrangement is highly desirable.
The present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the present invention a hydraulic system is provided and includes a pressurized fluid supply, a plurality of non-priority elements each including a signal port and a supply port, at least one priority implement including a signal port and a supply port and a priority valve arrangement. The priority valve arrangement is adapted to receive fluid from the pressurized fluid supply and selectively apportion fluid between the supply port of the priority implement and the supply ports of the plurality of non-priority elements. The valve arrangement includes a signal circuit operative to establish a flow priority between the priority implement and the plurality of non-priority implements and the signal circuit is in fluid communication with the priority supply. The signal circuit includes a pilot portion and a dynamic load portion and the signal port of the priority implement is in fluid communication with the priority valve arrangement through the dynamic load portion of the signal circuit. The signal ports of the plurality of non-priority implements are in fluid communication with the priority supply, wherein the dynamic load signal and the load signal are substantially prevented from fluid communication with one another to provide a stabilized dynamic load signal.